During the life of a subterranean well such as those drilled in oilfields, it is often necessary or desirable to perform services on the well to, for example, extend the life of the well, improve production, access a subterranean zone, or remedy a condition that has occurred during operations. Coiled tubing is known to be useful to perform such services. Using coiled tubing often is quicker and more economic than using jointed pipe and a rig to perform services on a well, and coiled tubing permits conveyance into non-vertical or multi-branched wellbores.
While coiled tubing operations perform some action deep in the subsurface of the earth, personnel or equipment at the surface control the operations. There is however a general lack of information at the surface as to the status of downhole coiled tubing operations. When no clear data transfer is possible between the downhole tool and the surface, it is not always possible to know what the wellbore condition is or what state a tool is in.
Coiled tubing is particularly useful for well treatments involving fluids, with one or more fluids being pumped into the wellbore through the hollow core of coiled tubing or down the annulus between the coiled tubing and the wellbore. Such treatments may include circulating the well, cleaning fill, stimulating the reservoir, removing scale, fracturing, isolating zones, etc. The coiled tubing permits placement of those fluids at a particular depth in a wellbore. Coiled tubing may also be used to intervene in a wellbore to permit, for example, fishing for lost equipment or placement or manipulation of equipment in the wellbore.
In deploying coiled tubing under pressure into a wellbore, the continuous length of coiled tubing passes through from the reel through wellhead seals and into the wellbore. Fluid flow through coiled tubing also may be used to provide hydraulic power to a toolstring attached to the end of the coiled tubing. A typical toolstring may include one or more non-return valves so that if the tubing breaks, the non-return valves close and prevent escape of well fluids. Because of the flow requirements, typically there is no system for direct data communication between the toolstring and the surface. Other devices used with coiled tubing may be triggered hydraulically. Some devices such as running tools can be triggered by a sequence of pulling and pushing the toolstring, but again it is difficult for the surface operator to know the downhole tool status.
Similarly, it is important to be able to accurately estimate the depth of a toolstring in a wellbore. Direct measurement of the length of coiled tubing attached to a tool string and injected into a wellbore may not accurately represent the toolstring depth however as coiled tubing is subject to helical coiling as it is fed down the well casing. This helical coiling effect makes estimating depth of the tool deployed on coiled tubing unpredictable.
The difficulty in gathering and conveying accurate data from deep in the subsurface to the surface often results in an incorrect representation of the downhole conditions to personnel that are making decisions in regard to the downhole operations. It is desirable to have information regarding the wellbore operations conveyed to the surface, and it is particularly desirable that the information be conveyed in real-time to permit the operations to be adjusted. This would enhance the efficiency and lower the cost of wellbore operations. For example, the availability of such information would permit personnel to better operate a toolstring placed in a wellbore, to more accurately determine the position of the toolstring, or to confirm the proper execution of wellbore operations.
There are known methods for transferring data from wellbore operation to the surface such as using fluid pulses and wireline cables. Each of these methods has distinct disadvantages. Mud pulse telemetry uses fluid pulses to transmit a modulated pressure wave at the surface. This wave is then demodulated to retrieve the transmitted bits. This telemetry method can provide data at a small number of bits per second but at higher data rates, the signal is heavily attenuated by the fluid properties. Furthermore, the manner in which mud-pulse telemetry creates its signal implicitly requires a temporary obstruction in the flow; this often is undesirable in well operations.
It is known to use electrical or wireline cables with coiled tubing to transmit information during wellbore operations. It has been suggested, as in U.S. Pat. No. 5,434,395, to deploy a wireline cable with coiled tubing, the cable being deployed exterior to the coiled tubing. Such an exterior deployment is operationally difficult and risks interference with wellbore completions. The need for specialized equipment and procedures and the likelihood that the cable would wrap around the coiled tubing as it is deployed makes such a method undesirable. Another technique, such as taught by U.S. Pat. No. 5,542,471 relies upon embedding cable or data channels within the wall thickness of the coiled tubing itself. Such a configuration has the advantage that the full inner diameter of the coiled tubing can be used for pumping fluids, but also has the significant disadvantage that there is no convenient way to repair such coiled tubing in the field. It is not uncommon during coiled tubing operations for the coiled tubing to become damaged, in which case the damaged section needs to be removed from the coil and the remaining pieces welded back together. In the presence of embedded cables or data channels, such welding operations can be complicated or simply unachievable.
It is known to deploy wireline cable within coiled tubing. Although this method provides certain functionality, it also has disadvantages. Firstly, introducing cable into the coiled-tubing reel is non-trivial. Fluid is used to transport the wireline cable into the tubing, and a large, high-pressure capstan is needed to move the cable along with the fluid. U.S. Pat. No. 5,573,225 entitled Means For Placing Cable Within Coiled Tubing, to Bruce W. Boyle, et al., incorporated by reference, describes one such apparatus for installing electrical cable into coiled tubing
Beyond the difficulty of installing a cable into coiled tubing, the relative size of the cable with respect to the inner diameter of the coiled tubing as well as the weight and the cost of the cable, discourage the use of cable within coiled tubing.
Electrical cables used in coiled tubing operations are commonly 0.25 to 0.3 inches (0.635 to 0.762 cm) in diameter while coiled tubing inner diameters generally range from 1 to 2.5 inches (2.54 to 6.350 cm). The relatively large exterior diameter of the cable compared to the relatively small inner diameter of the coiled tubing undesirably reduces the cross-sectional area available for fluid flow in the tube. In addition, the large exterior surface area of the cable provides frictional resistance to fluid pumped through the coiled tubing.
The weight of wireline cable provides yet another drawback to its use in coiled tubing. Known electrical cables used in oilfield coiled tubing operations can weigh up to 0.35 lb/ft (2.91 kg/m) such that a 20,000 ft (6096 cm) length of electrical cable could add an additional 7,000 lb (3175 kg) to the weight of the coiled tubing string. In comparison, typical 1.25 in (3.175 cm) coiled tubing string would weigh approximately 1.5 lb/ft (12.5 kg/m) with a resulting weight of 30,000 lb (13608 Kg) for a 20,000 ft (6096 cm) string. Consequently, the electric cable increases the system weight by around 25%. Such heavy equipment is difficult to manipulate and often prevents installation of the wireline equipped coiled tubing in the field. Moreover, the heaviness of the cable will cause it to stretch under its own weight at a rate different from the stretch of the tubular, which results in the introduction of slack in the cable. The slack must be managed to avoid breakage and tangling (“birdnesting”) of the cable in the coiled tubing. Managing the slack, including in some cases trimming the cable or cutting back the coiled tubing string to give sufficient cable slack, can add operational time and expense to the coiled tubing operation.
There are other difficulties with using a wireline cable inside coiled tubing for data transmission. For example, to retrieve the data off the transmission line in the cable, a data collector is needed that can rotate with the reel while simultaneously not tangling up that part of the wire which is outside the reel (e.g., that wire that is connected to a surface computer). Such known devices are failure prone and expensive. In addition, the cable itself is subject to wear and degradation owing to the flow of fluids in the coiled tubing. The exterior armor of the cable armor can create operational difficulties as well. In some well operations, the coiled tubing is sheared to seal the wellbore as soon as possible. Shears optimized to cut through coiled tubing however typically are not efficient at cutting through the armored cable.
From the foregoing, it will be apparent that the need exists for systems and methods to gather and convey data to and from wellbore operations using coiled tubing to the surface without encumber the wellbore operations. Systems and methods to gather and convey this information in a timely, efficient and cost effective manner are particularly desirable. The present invention overcomes the deficiencies in the prior art and addresses these needs.